The invention relates generally to the manufacture of ortho-rhombic litharge (yellow lead oxide) and in particular to a process for the continuous refining of litharge and a loopreactor for the refining of litharge.
Litharge is an important article of commerce, used on a large scale in a number of industrial manufacturing processes. High purity litharge, for example containing less than 0.01% metallic lead, is typically required.
Litharge of sufficiently high purity for use in the glass industry has been manufactured by the Barton pot process for many years. In this process, lead is molten and fed to the Barton pot where it is agitated and contacted with air at a temperature up to 600° C. In the Barton pot, the pool of molten lead is stirred by high speed blades. This throws up droplets which are oxidized by the air, but the oxidation is incomplete. The solid powder product, containing from about 70 to 99% PbO, is entrained in the air stream while the heavier lead doplets fall back into the pool.
The Barton pot process is limited by the requirement for multiple steps, involving an expensive train of equipment, and also by the fact that the maximum size of a Barton pot is limited, which frequently creates the need for a number of Barton pots to achieve a desired production level. The Barton pot process and other prior art processes are described in “LEAD OXIDES—Chemistry—Technology—Battery Manufacturing Uses—History” (1974), Independent Battery Manufactures Association, Inc., Florida USA, at pages 21 to 25. Reference is made to Barton's U.S. Pat. Nos. 988,963 (1911) and 1,060,153 (1913), Pope and Barton U.S. Pat. No. 633,533 (1899), Mayer 2,235,487 (1941), and Vehernkamp et al. 3,322,496 (1967).
In describing a “fused litharge furnace” with reference to Hughes U.S. Pat. No. 975,955 (1910) and Petraeus U.S. Pat. No. 592,594 (1897), which is said to be “now mainly of historical interest” this book comments that “A mixed bath of lead and litharge at about 1000° C. has almost fantastic corrosive and erosive properties” which has caused major problems.
The book also describes the “fume type process”, which produced a “smoke” from which a product of fine particle size was recovered in a baghouse. (Calbeck U.S. Pat. No. 1,511,215 (1924) and Garesche U.S. Pat. No. 2,065,218 (1936)).
U.S. Pat. No. 3,648,936 relates to a constant acceleration fluid energy mill. Said fluid energy mill is comprising a lower inlet section and an upper classification section connected by a vertical upstack on one side and a vertical downstack on the other side, the inlet section having tangential nozzles connected to a source of gaseous fluid pressure and a raw feed inlet, whereby the raw feed particles are entrained and centrifugally whirled around the mill by the pressure fluid. The portion of the inlet chamber adjacent the upstack, as well as the upstack itself and the portion of the classification chamber adjacent the upstack form part of an antifriction curve. The classification section is preferably generally circular and has at least one exhaust outlet in the center so that the lighter particles on the inner periphery of the centrifugal path are rotated in a helical path until exhausted through the outlet. Preferably, nozzles are provided in the classification section to project pressure fluid thereinto in a generally elliptical path.
However, in view of the high density of litharge the direct adaption of said fluid energy mill for the refining of litharge is impossible. One of the important problems in the technology of refining litharge is the dosage of litharge to provide a constant flow in a continuous reactor.